2.9 bucking under load, high/low idle

[DangaRanger]

1990 2.9 manual, truck is bucking under load at any speed and in any gear, I have replaced Map sensor, TPS, IAC to no luck.... I unplugged TPS and truck no longer bucks and runs like new.... what am I missing here ?

 

[franklin2]

Take it for a spin and get it fully warmed up. Bring it back home and while it's idling in the driveway, unplug the IAC plug. The idle should slow but not stall out. If it stalls out, turn the idle stop screw in till the engine idles about 400-500 rpm. If when you pull the plug the idle stays the same, it's too fast. Turn it down. This will put your throttle position idle voltage more in line, and make the dashpot feature start working again. See if that helps it.

 

[DangaRanger]

Take it for a spin and get it fully warmed up. Bring it back home and while it's idling in the driveway, unplug the IAC plug. The idle should slow but not stall out. If it stalls out, turn the idle stop screw in till the engine idles about 400-500 rpm. If when you pull the plug the idle stays the same, it's too fast. Turn it down. This will put your throttle position idle voltage more in line, and make the dashpot feature start working again. See if that helps it.

Will have to give this a try Wednesday, I tried this at first to test the IAC before I replaced it and it passed but had a new one already so I replaced it, I have a new ignition control module coming I will try that as well and see if there is any issues as for it is only happening once the engine reaches operating temps.

 

[DangaRanger]

UPDATE, new ignition control module fixed all issues. Truck is running fine even with A/C on under load.

 

[franklin2]

UPDATE, new ignition control module fixed all issues. Truck is running fine even with A/C on under load.

Good old TFI. Glad you got it fixed.

 

[DangaRanger]

Franklin2 I appreciate the input you gave me as well.